1. Field of the Invention
The present invention relates to a hybrid cooling plant including at least one sector with a dry cooling part connected to a feed pump and including at least two heat exchangers which are connected in parallel, and with a wet cooling part located underneath the dry cooling part, wherein the dry cooling part and the wet cooling part are connected to each other by a closed connection or linkage, wherein the highest locations of the heat exchangers are connected through a deaerating line to a vacuum pump and the heat exchangers are provided with evacuating and ventilating valves and level limit switches.
2. Description of the Related Art
A hybrid cooling plant has at least one sector with a dry cooling part and a wet cooling part. Several sectors may be arranged in rows one behind the other in the form of individual hybrid cooling towers. These hybrid cooling towers usually have a rectangular cross-section in the horizontal direction. However, the sectors may also be components of a single hybrid cooling tower which has a round or polygonal cross-section in the horizontal direction. Independently of the fact whether the sectors are arranged in rows one behind the other or on a circle, it is usually the case that the water to be cooled is applied in parallel to all sectors.
Each sector is composed of a dry cooling part with at least two heat exchangers and a wet cooling part with dripping elements underneath the heat exchangers. Cooling air is supplied, if necessary forcibly, to the dry cooling part as well as to the wet cooling part. The water to be cooled is first conducted by means of a feed pump through the dry cooling part and is subsequently conducted through a closed connection to the wet cooling part in order to save pumping energy. From the wet cooling part, the cooled water drops into a water collection basin arranged underneath the wet cooling part.
For controlling the output especially of a hybrid cooling plant composed of several sectors or for maintenance or repair purposes, it is known in the art to temporarily switch off individual sectors, several heat exchangers of a sector or also individual heat exchangers; in other words, these elements are taken out of the cooling operation. When a hybrid cooling plant is first taken into operation, the feed pump which forces the water to be cooled into the hybrid cooling plant causes the water to be forced up to the highest locations of the heat exchangers; this is because of the operational characteristics of the feed pump and the fact that all heat exchangers are of equal construction; on the other hand, when the operation of a sector or heat exchanger which has been switched off is restarted, it is necessary to fill each of the switched-off heat exchangers again with water. For this purpose, a vacuum pump is used which produces a negative pressure. Such a vacuum pump is also required for maintaining the closed connection (siphon effect) between the dry cooling part and the wet cooling part. A common vacuum pump is required at least for all heat exchangers of the hybrid cooling plant. This vacuum pump is then connected through various deaerating lines to the highest locations of the heat exchanger, so that a complete deaeration is effected.
To ensure that, when the operation is restarted, the vacuum does not draw the water into the deaerating lines and becomes flooded, each heat exchanger is provided with suitable level limit switches and evacuating and ventilating valves. Since, in principle, each heat exchanger is provided with a level limit switch, an evacuating valve coupled to the level limit switch and a deaerating valve, this means that hybrid cooling plants with usually several sectors have a comparatively large number of valves. Added to this is the fact that expensive line mechanisms and the electronic remote control are required. This large amount of valves not only results in significant costs for procuring, connecting and maintaining the plant, but there is the additional danger that the entire evacuating plant will be inoperative when only a single valve fails.